Critical circuits within a complex electronic system require a highly reliable source of regulated power. Such systems typically employ several power supplies, active and backup power supplies, to provide the required reliability. A conventional method of combining redundant power supplies uses diodes to "Or" the outputs of the power supplies. To regulate the level of the voltage that is being supplied to the drain (load), the voltage at the drain is sensed and fed back to each of the redundant power supplies. As will be explained below in detail, each such power supply compares the value of the sensed signal with the value of a respective preset signal and changes its output as a function of the difference between the sensed and preset signal. Such regulation may have the effect of causing the output voltage level of one of the power supplies (typically the backup power supply) to decrease significantly, while the other power supply outputs an acceptable voltage level. Apparatus that monitors the backup power supply would thus be unable to determine if that power supply is operating properly, and, more likely, would incorrectly conclude that the backup supply has failed.